1. Field of the Invention
This invention relates to the storage of spent nuclear fuel, and more particularly to the use of concrete for such storage.
2. Description of the Prior Art
Many nuclear reactors utilize fuel in the form of pellets encased in metallic cladding. These rods may be bundled in a duct-type structure, or integrated through a skeletal structure which includes grids spaced along the assembly length. Upon discharge of such assemblies from a nuclear reactor, the fuel rods contain not only fission products in the form of solids and gases, but also fissionable isotopes which are useful as fuel in reactors subsequent to reprocessing.
Typically fuel assemblies are discharged from the reactor and placed within a water filled spent fuel storage pool which serves as a source of thermal cooling and also radiation shielding. These pools, however, are in relatively short supply and, because of the lack of sufficient reprocessing facilities, such pools cannot provide the long-term storage presently needed. Further, underwater storage may not provide acceptably long-term stability for storage, and long-term storage facilities either above ground or in geologically stable underground structures are presently being considered. The proposed solutions, however, have not been publically accepted to date.
Accordingly, it is desirable to provide alternative systems for intact storage of spent nuclear fuel. A preferable system for storage will meet the following requirements. The radioactive materials in the spent fuel must be contained, and leaching of the encapsulated fuel and breaching of the encapsulation must not occur over an extended period of storage time. The encapsulation must permit adequate removal of the heat of radioactive decay so as not to allow the fuel to reach temperature levels that would endanger the integrity of its containment. It is further advantageous to have the encapsulation system providing sufficient shielding for the protection of associated structures and personnel against gamma and neutron radiation emitted from spent fuel rods. It may prove to be additionally advantageous to have such systems provide the ability for relatively easy removal of the spent fuel from its containing structure subsequent to a predetermined amount of radioactive decay and at a time when the spent fuel is desired for reprocessing and retrieval of desired isotopic species. Alternatively it may be desirable to provide storage systems which provide a substantial degree of difficulty regarding retrieval of or accessibility to the fuel so as to alleviate the potential for terrorist and diversion activities. And, because of the substantial need for such storage systems on a short-term time period, it is desirable to utilize near state-of-the art technology to provide reliable encapsulation systems available within a short period of time.